This study is a cooperative, randomized trial to determine the efficacy of Vi polysaccharide in preventing typhoid fever in Nepal. The Biometry Branch's involvement in this study is to design data collection forms, and assist in the data management and the analysis with the study investigators from NICHD and Nepal. In October, a pilot study was done to verify the immunogenicity of the vaccine. The analysis of this data was performed by the Biometry Branch. In March 1986, 6,912 volunteers from five villages in Nepal were randomly vaccinated with either the Vi polysaccharide or pneumonococcal vaccine. These volunteers will be visited every three days for the next two years to verify their health status and to detect any typhoid cases prior to treatment. Blood cultures will be done on anyone with a fever of three days duration. The results of the randomization will not be available until late in 1988.